Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $192.88   6.143%   $204.7286   $204.73   $204.75   $204.70  
  Purchase #2 $107.79   13.592%   $122.4408   $122.44   $122.45   $122.40  
  Purchase #3 $22.54   13.263%   $25.5295   $25.53   $25.55   $25.50  
  Purchase #4 $91.87   12.436%   $103.295   $103.30   $103.30   $103.30  
  Purchase #5 $248.46   7.732%   $267.6709   $267.67   $267.65   $267.70  
  Purchase #6 $135.78   7.535%   $146.011   $146.01   $146.00   $146.00  
  Purchase #7 $33.34   12.145%   $37.3891   $37.39   $37.40   $37.40  
  7 purchase totals = $832.66       $907.0649   $907.07   $907.10   $907.00